Cross-talk reduction



April 7, 1931.

M. A. WEAVER CROSS TALK REDUCTION Filed Oct. 2 6, 1928 Zluo-wire Repeater INVENTOR BY 715mm Patented Apr. 7, 1931 erre- MYRoN A. W AVER, or RYE, NEW YORK, AssIGNoR T0 AMERICAN TELEPHONE AND TELEGRAPH COMPANY, A CORPORATION or NEW YORK CROSS-TALK REDUCTION Application filed October 26, 1928. Serial No. 315,255.

This invention relates to a method and means for reducing crosstalk between telephone circuits, particularly telephone circuits in cable.

In cable circuits thehconductors are arranged in groups of four called a squad. Each group offour conductors serves for carrying three ordinary telephone conversations, one pair of conductors forming one socalled side circuit, the other pair forming another so-called side circuit and the conductors of each pair when connected in parallel forming one side of a so-called phantom circuit. From'thestandpoint of crosstalk, it is desirable to reduce as far as practicable the number of sections, of cable between repeater points in which any two of these circuits are carried in the same cable quad. For example, if two cable circuits, say one phantom and one side circuit, are routed over the conductors of theisame quad thoughthe entire system from end to end, the crosstalk from one end to the other, due to their adjacent relation, is augmented in eachrepeater section and will be obviously much greater than if the same twocircuits are only routed over the conductors of the same quadthrough one repeater section. If the two circuits in question have their connections shifted at each repeaterpoint so that a given one of the circuits will only be related to the other in close crosstalk relation throughout one repeater section, and throughout each successive repeater section is related to entirely difierent circuits in the same cable, the crosstalk in the. first circuit will be relatively small from each of the other circuits with which it is re lated. While the total crosstalk may be as great as though the circuits were routed in the same relation throughout the entire system, it will be made up of a number of small components from a number of different circuits so that the resultant crosstalk is not in telligible but is in the nature of unintelligible noise. I i q I ,Ifall of the circuits are treated in this manner any particular circuit will no longer receive crosstalk in a large number of re-, p'eater sections ,from any given circuit in the same quad with it, but will receive crosstalk from many circuits any one or which is in the same quad with it for only one repeater section. The crosstalk overheard in each circuit will then consist of a multiplicity ofrelatively weak conversations, and the chance of understanding any one conversation taking place on another circuitrwill be much reduced. i

The method of cross-connectin g the circuits in accordance with the present invention results in an approach to the desirable condition of equal and'very slnall crosstalk from all of the circuits in the cable into any one circuit. Observations on circuits arranged in accordance with the present invention have shown that a condition is approached where there is practically no intelligent crosstalk but simply i. unintelligible noise. The system has in addition to the advantages above outlined the further advantage that i the inter-connectionof the circuits at the repeater stations gives a considerable reduction in the ratio between maximum and average noise (including "crosstalk, efi'ects) In other words, consideringa group of circuits,

the noisiest circuit ofthe group will not be considerably noisier thanthe average for the whole group. 7 r r v In shifting the connections at the repeater point in a manner to accomplish theresults above outlined, itis, of course, necessary to usefthe best methods known in the art in construction,installation and maintenance, for the purpose'of limiting the maximum values of crosstalk between the side circuits and between'the phantom and side circuits of each quad in a singlejrepeater section. Furthermore, the best methods knownin the art must be used to limit the maximum values of crosstalk between circuits of difieren't quads in the same repeater section. In short, the method and arrangement of the present invention are intended to supplement the best known practices of the art from the standpoint ofjreducing crosstalk so that not only the crosstalkreduction due to these prior methods obtains but the advantages of the present invention in addition. a 1 .'Ihe invention may now be more fully understood from the following detailed descripcar tion thereof when read in connection with the accompanying drawing, Figure 1 of which is a symbolic representation of how the side and phantom circuits of each quad of a group of quads in a cable may be crossconnected and re-routed at each successive repeater point in accordance with the present invention, while Figs. 1a and 16 show respectively the symbol representing the connection between a phantom and its two associated side circuits, and the symbol representing a two-wire repeater. In Fig. 1 of the drawing each pair of conductors constituting a side circuit is represented, for the sake of simplicity, by a single line instead of a pair of lines one for each conductor.

deferring to Fig. 1, which shows a schematic layout in accordance with the invention, it is assumed that a cable extends between terminal points A and E through repeater points B, C and D. This cable may include any desired number of quads, of which, for purposes of illustration, six quads, each involving two side circuits of two conductors each and a common phantom, are treated as a group. In order to accomplish the purpose of the present invention the connections of each side circuit of a quad are shifted at each repeater point so that each side circuit will be connected to the conductors of other side circuits in different quads. Likewise, the connections are so shifted that the phantom, while in effect continuing straight through from section to section, is, due to the cross-connection of the side circuits, actually associated with a dilferent pair of side circuits in each successive repeater section.

In making the cross-connections involved, the pairs corresponding to each side circuit are numbered in regular order, and in the case illustrated in Fig. 1 these numbers run from 1 to 12, inclusive, although the method is applicable independently of the number of quads to be treated and of the number of repeater stations in the system. The phantom circuits, as already stated, are so connected as to proceed straight through each repeater station. The side circuits, however, incoming from each preceding repeater (or terminal) are connected individually to the repeaters of the next lowerodd numbered side circuits, if they are normally connected to odd numbered side circuits, or to the repeaters of the next higher even numbered side circuits if they normally connect to even numbered side circuits. The repeater that was normally connected to the highest odd numbered side circuit in the group (which in the case assumed. is 11) is connected to the lowest odd numbered side circuit (1), while the repeater that was normally connected to the lowest even numbered side circuit (in this instance 2) is connected to the highest even numbered side circuit (12) inthe group. In short, the even numbered side circuits in the group have their connections shifted or rotated in one direction and the odd numbered side circuits have their connections shifted or rotated in the opposite direction.

If we now consider the phantom which in the first section from A to B is superimposed on side circuits 1 and 2, we find that in the section from B to C it is superimposed upon side circuits identified as 3 and 12 at sta tion A, while in the section from C to D this same phantom is superimposed upon side circuits which are identified as 5 and 10 at station A, etc. Likewise, considering the side circuit 1 at station A, while it is in the same quad with side circuit 2 in the section from A to B it is in the same quad in the section from B to C, with what was originally side circuit 10, and in the same quad in the section from C to D, with what was originally side circuit 6, etc.

In two-wire circuits it is desirable and usually necessary to rotate the connections at each repeater station in a certain unit such as a regulator section. At the ends of these circuit lengths it is also desirable to provide these special cross-connections in cases where this can be done without undue difi'iculty. In four-wire circuits satisfactory crosstalk conditions will normally prevail if the rotation of connections is carried out only at the ends of regulator sections (each of which would include a number of repeater sections). This is because in four-wire circuit arrangements the circuits transmitting in one direction are all arranged in one group and those transmittin in the opposite direction in another group. Since the transmission on the three units of a quad in four-wire circuits is always in the same direction, the energy levels on the three units are about the same, and crosstalk between the units is not amplified to the extent it is when the units may transmit in opposite directions as in two-wire circuits. In four-wire circuits the condition does not arise, however, in which the sending end of a circuit is crosstalking into the receiving end of a circuit in the same quad and thereby competing in the latter with the attenuated currents transmitted fron'i the sending end thereof. In four-wire circuits, therefore, the cross-connections in accordance with the present invention need not be made as frequently as in the case of two-wire circuits.

With two-wire circuit groups rotated de-- scribed above no side-to-phantom duplications will be experienced in a given length of cable providing the number of quads in the rotated group at least equal to the number of sections between repeaters. There will, however, be a duplication of side-to-side crosstalk exposure if the number of quads is side circuits 1 and 2,-if1we trace these side circuits through stations B, C and D, which includethree repeater sections, we do not find these same side circuits arranged in the same quad again until after they havefpassed through repeater pointD, wheat-hey will then be associated inthe cable'sectionbetweenD andE in the quad comprising the side circuits identified at station A as numbers? and 8. .Lik'ewis side circuits 7 and 8 at station A do not appear in the same quad again until they arriveat station D, where they will again be together in the quad comprising the. side circuit. conductors identified as land 2 at station D. Thus, it is apparent'that to avoid duplication of side-toside crosstalk exposure in more than one repeater section the number of quads in the group to be rotated must be at least twice as great the number, of repeater sections.

Fromfthe. standpoint ofphantom-to-side cross talk, howeverqno duplications will occur, as already stated, if the number of repeater sections does not exceed the number of quads in the group. F or example, let us consider the phantomcircuit which is superposed at station A'upon side circuits 1 and 2.

Between-A and Bthis plantom isassociated in intimate crosstalk relation with side circuit 1; between B and C it is associated with the side, circuit which isidentified as 3 at station Agubetween C and D it is associated with theside circuitjidentified as 5121i? station A between D and E it is associated with the side circuit identified as 7 at station A. If

we consider theprocess of cross connection as being extended through SUCCGSSlVB repeatcircuit 1 more than once. If, however, the

system is extended on .to a succeeding station H, then between stationsG and IIthe phan-' tom under consideration will againbe associated with the side circuit originally idens tified as l at station A in the same relation as existed between A andB.

From the foregoing. it is evident that to prevent side-to-side duplication twice as many quadsmust be included in the crossconnecting arrangement as is necessary to preif the layoutisfsufiicient-to prevent duplica tion'of side-tosphantom crosstalk a more complicatedschemewould not be justified in order to prevent duplication: of side to side crosstalk exposure.

"In general, it isof. course desirable that the .numberof phantom groups of circuits involvedin a given rotation group should be as large as-conditions will permit. On the other hand, where different conditions obtain it may. be advantageous from the standpoint of circuit flexibility-to limit thenumber of quads "in a rotatable group to a moderately small number as, for example, from four to six quads. This,-of course, willnot result in duplication of exposures where the system is comparatively short, and under such conditions a given cable may have its total number of quads divided up into a number of separate rotation groups. In any event, it is in general desirable that the number of quads-involved I in a given rotation scheme should be the'same throughout the same regulator section.

It willbe obvious that thegeneral princi ples herein disclosed may be embodied in many other organizations widely different from those illustrated without departing from the spirit otthe'invention as defined in the following. claims. 1 i

:IVhat is claimed is: 1 I i 1." In a cable system the conductors of which are arranged in a plurality of quads, each quad comprising a pair of side circuits upon which a phantom circuit is superimposed, the method of reducing the effect of crosstalkwvhich consist-s in shifting the connectionsof theconductors'of the quads and =9 thephantom circuits at each of a plurality of junction points between cable sections so as to superimpose the phantom upon a di-fierent pair of sidecircuits in each of a plurality of successive sections i v 2. In a a cable, system the conductorsof which are arranged in a plurality of quads, each quad comprising a pair of side circuits upon whicha phantom circuitis superimposed, the method o'freducing-the eiiect ot' crosstalk which consists in shifting the connectionsoi the conductors of the quads at each of more than two junction points between cable sections without shifting the phantom connections so that each side circuit of any given quad in one section will be routed through successively different quads in each of more than twosu'cceeding sections and the phantom will be superposed on different side circuits in different sections.-

I '8. In a cable system the conductors ofwhich are arranged in a plurality of quads, each quad comprising a pairof side circuits uponwhich a phantomcircuitis superimposed, the'method of reducing the efi'ect of crosstalkwhichconsists in shiftingthe connections of the'conductors of thequads and the phantom circuits at each ofa plurality of junction points between cable sections so'tha't each side circuitot-any given quad in one section will be routed through different quads in each of a plurality of succeeding sections and each phantom circuit will be superposed upon a difierent pair of side circuits in each of a plurality of successive sections.

4. In a cable system the conductors of which are arranged in a plurality of quads, each quad comprising a pair of side circuits upon which a phantom circuit is superposed, and in which correspondingly numbered quads are grouped in each'succeeding section, the method of reducing the eiiect of crosstalk which consists in shifting the connections of the conductors of the quad at each of a plurality of junctions between sections so that one side circuit of each quad will be connected to the corresponding side circuit of a quad of a succeeding numerical order in one direction in the next cable section, and the other side circuit of each quad will be connected to the corresponding side circuit of a quad of a succeeding numerical order in the opposite direction.

5. In a cable system the conductors of which are arranged in a plurality of quads, each quad comprising a pair of side circuits upon which a phantom circuit is superposed, and in which correspondingly numbered quads are grouped in each succeeding section, the method of reducing the effect of crosstalk which consists in shifting the connections of the conductors of the quad ateach 01'' a plurality of junctions between sections so that one side circuit of each quad will be connected to the corresponding side circuit of a quad of a succeeding numerical order in one direction in the next cable section, and the other side circuit of each quad will be connected to the corresponding side circuit of a quad of a succeeding numerical orderin the opposite direction, and connecting the conductors of the phantom circuit of each quad of one section to the phantom conductors. of the corresponding quad oi the succeeding section at each junction point between sections.

6. A cable system comprising a plurality of cable sections each comprising a plurality of conductors arranged in quads, each quad comprising a pair of side circuits and a phantom circuit superposed on the pair of side circuits, the conductors of the side circuits and the phantom of each quad of each section being cross-connected to the conductors of the side circuits and phantoms of the quads of the succeeding section so as tosuperpose the phantom of each quad upon a diiierent pair of side circuits in each of a plurality of successive sections. I

7 A cablesystem comprising a plurality of cable sections each comprising a plurality of conductors arranged in quads, each quad comprising a pair of sidecircuits andta phantom circuit superposed on the pair of side circuits-,the conductors of the side circuits ot'ea'ch quad to'each'section'heiug cross-connected to the conductors of the side circuits of the quads 01": the succeeding section Without shifting the phantom connections so that each side circuit of any given quad in one section will be successively routed over conductors of diiierent quads in each of more than two succeeding sections and the phantom will be superposed on diiierent side circuits in diiierent sections.

8. A cable system comprising a plurality of cable sections each comprising a plurality of conductors arranged in quads, each quad comprising a pair of side circuits and a phantom circuit superposed on the pair of side circuits, the conductors of the side circuits and the phantom of each quad of each section being cross-connected to the conductors of the side circuits and phantoms of the quads of the succeeding section so that each side circuit of any given quad in one section will be routed over conductors of diiierent quads in each of a plurality of succeeding sections, with the phantom of each quad of a given sec tion superposed upon a different pair of side circuits in each of a plurality of successive sections.

9. A cable system comprising a plurality of cable sections each comprising a plurality of conductors arranged in quads, each quad comprising a pair of side circuits and a phantom circuit superposed on the pair of side circuits, a corresponding number of quads of each section being grouped and numbered so that the quads in a group'in each section will be correspondingly numbered in the same successive order in each section, the conductors of the side circuits of each qua-d of a group in each of a plurality of cable sections being cross-connected to conductors of quads of the corresponding group of the next section so that one side circuit of each quad of the group will be connected to the corresponding side circuit of a quad of succeeding numerical order in one direction in the next cable section, and the other side cir cuit of each quad of the group will be connect-ed to the corresponding side circuit of quad of succeeding numerical order in the opposite direction.

10. A cable system comprising a plurality of cable sections each comprising a plurality of conductors arranged in quads, each quad comprising a pair of side circuits and a phantom circuit superposed on the pair of side circuits, a corresponding number of quads of each section being grouped and numbered so that the quads in a group in each section will be correspondingly numbered in the same successive order in each section, the con ductors of the side circuits of each quad of a group in each of a plurality of cable sections being cross-connected to conductors of quads of the corresponding group of the next section so that oneside circuit of each quad o'f'the group will be conne'cted to'the airesponding side circuit of a quad of succeeding numerical order 1n one direction in the next cable section, and the other s1de circult of each quad of the group will be connected to, the corresponding side circuit of a quad of succeeding numerical order in the opposite direction, and the conductors of the phantom of each quad in a group of one cable section being connected to the phantom conductors of the corresponding quad of the group of the succeeding section at each junction point between sections.

-11. In a cable system the conductors of which are arranged in a plurality of quads, each quad comprising a pair of side circuits upon which a phantom circuit is superposed, the method of reducing the effect of crosstalk which consists in shifting in eifect the connections of the phantom circuits at each of a plurality of junction points between the cable sections so as to superimpose the phantom upon a different pair of side circuits in each of a plurality of successive sections.

In testimony whereof, I have signed my name to this specification this 24th day of October, 1928.

MYRON A. WEAVER. 

